Electrical energy can be harvested or generated using a variety of techniques. For example, an energy source can include a mechanical-to-electrical conversion device such as a piezoelectric energy harvesting (PEH) device. Another example of an energy source can include a photovoltaic (PV) device, such as a solar cell or a solar array. Yet another example of an energy source can include a thermo-electric generator (TEG). Use of a PEH device, PV device, a TEG, or other energy sources can include coupling such an energy source to a load to provide operating energy for the load. However, there can be a detrimental effect on energy conversion efficiency or power transfer efficiency if the load current or voltage requirements are badly mismatched to the output characteristics of the energy source.